J. Am. Chem. SOC.1986, 108, 4230-4232
4230 Table I. Preparation of Vinylcopper Reagents
%
olefin
M
R&F=CFCu
yield'
Cd CFZ=CFCu CF,=CFI Zn CFZ=CFCu CF,=CFBr Cd (Z)-CF~CF=CFCU (Z)-CF,CF=CFI Zn (Z)-CF&F=CFCu (Z)-CF3CF=CFI Cd (E)-CF,CF=CFCu (E)-CF$F=CFI Cd (Z)-CF~(CF~),CF=CFCU (Z)-CF3(CF2)4CF=CFI Cd (Z)-CF$CI=CFCu (Z)-CF,CCI=CFI CF,C(Ph)=CFBr Zn CF,C(Ph)=CFCu E/Z = 59/41 E/Z = 59/41 CF3CF=C(Ph)CF=CFBr Zn CF$F=C(Ph)CF=CFCu EIZ = 90110 E I Z = 90110 OOverall I9F NMR yield based on starting olefin.
99% 72% 92% 76% 83% 87% 78% 84% 63%
Scheme I' z*3cF-cFc(o)c~
(77s)
L.€*3CF.CFCFIC(Ph)CF3(5U)
t
2-CF3CFICFPh(56%)
a short induction period, a mild exotherm resulted and a mixture of mono and bis (2)-CF,CF=CFCdX was formed in 96% yield (mono/bis = 67/33) as determined by 19FNMR. The excess cadmium was removed by pressure filtration under dry nitrogen through a fine fritted glass filter (Schlenk funnel). Then 4.2 g (0.029 mol) of CuBr was added to this mixture at 0 O C and the mixture was stirred for 'I2h followed by warming to room temperature. 19F N M R analysiss indicated a 96% yield of (2)CF3CF=CFCu. This solution was employed for subsequent functionalization reactions. In summary, this work describes an unequiuocal route to fluorinated vinylcopper reagents. The reagent is readily produced in situ from vinylic halides under mild conditions, is easily scaled up, allows total stereochemical control, and can be directly utilized in a wide variety of synthetic transformations. Our work continues with these reagents and future efforts will focus on the elucidation of the full scope of these new organometallic reagents.
Acknowledgment. We thank the National Science Foundation (CHE-85-16380) and the Air Force Office of Scientific Research (AFOSR-85-0009) for financial support of this work. (7) Yields in Scheme I are based on I9FNMR using PhCF3 as the internal standard. (8) 19FNMR of 'CF, LF
exhibits the following spectroscopic parameters: Fa (dd) -64.7, Fb (dq) -135.9, and F, (dq) -180.0 ppm; J.b = 22.6, J., = 13.7, and Jbe= 100.2 Hz.
a copper(1) halide metathesis reaction of the corresponding vinylcadmium and/or zinc reagent^.^ Table I summarizes these preliminary results. RFCF=CFX+ M x = Br, I M = Cd, Zn DMF mom temperature60 OC
(RFCF=CF)ZM + MX2
RFCF=CFMX culx rMm
+
temperature' RFCF=CFCu
68-99% The preparation of the vinylcadmium or -zinc precursors proceeds stereospecifically, and the metathesis with Cu'X occurs with retention of codiguration? Consequently, stereochemial integrity is retained throughout the synthetic sequence and one can confidently prepare either isomeric copper reagent with total stereochemical control by proper choice of the appropriate vinyl halides6 The vinylcopper reagents exhibit excellent stability at room temperature in the absence of oxygen and/or moisture. At higher temperature (>50 "C) they undergo rapid decomposition. The vinylcopper reagents participate in a variety of alkylation, coupling, and acylation reactions as illustrated in Scheme I with (Z)-CF,C F-CFCU. The operational details of a typical experimental procedure for the pregeneration of (Z)-CF,CF=CFCu are outlined below: A two-necked 50-mL round bottom flask equipped with thermometer, magnetic stir bar, septum port, and condenser was charged under a nitrogen atmosphere with 6.5 g (0.025 mol) of (2)-CF,CF=CFI and 25 mL of dry DMF. To this solution was added 3.5 g (0.031 mol) of acid-washed cadmium powder. After (4) Such reagents are prepared in 80-991 yield via direct reaction of cadmium or zinc powder with the corresponding vinyl iodide (at room temperature) or vinyl bromide (at 60 "C) in DMF. ( 5 ) Stereochemical assignments are based on JFJor JF,CF in either the organometallic reagent or in the reduced olefin R&F=CFd, obtained on hydrolysis of the copper reagent. (6) In 1979 Miller and co-workers reported the preparation of (E)CF3CF300 "C) showing expected mass (M' m / z 937) and NMR ~ p e c t r a . ~The dl (D3)and meso (C3& structures were assigned to 2 and 3, respectively, because optically active (-)-5, [a]z50 -43O (CHCIJ, on reaction with HC02Hsimilarly afforded D and 3 for which no rotation could be mea(+)-2, [ a ] 2 5+49O, sured. As (-)-5 was prepared from knownI0 (M)-(+)-6 (>95% ee), the absolute configuration of 2 was established as shown on the formula.
'3
(-1
1
(+I 2
* CHCL3
6m
60 7
7.0
6.0
4.0
5.0
3.0
2.0
PPM
Figure 1. High-field 200.13-MHz ' H NMR spectrum of 2 (0.01 M) and CHCI, (0.02 M) in (CDCI,), at 300 K; the star indicates the residual C12CHCDCll solvent peak. The host resonances are broadened as a consequence of .the slow exchange between complexed and uncomplexed species having slightly different chemical shifts. The sharpness of the two CHCI, peaks is due to the large chemical shift difference (6, - 6, 890 Hz) of the free and complexed guest species with respect to the exchange rate (ca. 2.5 s-I).
C12)2at 300 K (Figure 1 ) and saturation transfer experiments revealed a slow exchange, on the 200-MHz spectrometer time scale, between the free and complexed CHC13 resonances, at bo 7.28 and 8, 2.84. On heating, these signals broadened, as the inclusion/exclusion process became faster, and vanished above -360 K (the fast exchange CHCl, peak could not be reached due to temperature limitation); cooling the sample down to 300 K restored the original spectrum. The huge upfield shift (A8 4.44) induced on the CHCl, resonance is consistent with an intramolecular inclusion of this guest in the cavity of 2 ("cavitate"). Thus 2 complexes reversibly CHC1, in (CDC12)2,and the apparentl2 stability constant of the 2.CHCl3 cavitate in this solvent was estimated from the appropriate peak areas to be K', 470 M-' (*lo%) at 300 K. From the line shape of the exchanging CHC1, peaks, the barriers for entrance and departure of the guest were evaluated (f0.5 kcal/mol) to be AG* (300 K) 13.4 and 17.2 kcal/mol, respectively. The plot of In K', vs. 1 / T in the range 297-330 K gave ( r 0.996) AH-6.9 kcal/mol and AS -1 1 cal/(mol K); complexation of CHC1, by 2 is thus strongly enthalpy driven while it is entropy disfavored. A similar behavior has been reportedzb for a bowl-shaped cavitand complexing CSz in CDCI,, although the cavitate stability was much weaker (13.2 M-I at 250 K). Similar experiments with the CHZCl2and CHBr, complexes yielded, at 300 K, the following values of K', (and 8o - 8-): 2CH2C12-100 M-I (4.15); 2-CHBr3 -40 M-I (4.36). Acetone, benzene, and ethanol were weakly complexed. Addition of 1 equiv of CC14 to the 2CHC1, complex in (CDCl,), did not detectably change the free/complexed CHC13peak ratio; only a 20-fold excess of CC14 slightly decreased this ratio; hence the 2.CCI4 cavitate must be perhaps 2 orders of magnitude weaker than the CHCl, one. The apparent stability ( K f S of ) the cavitates not only depends on the intrinsic stability of the host-guest supermolecules but also encompasses soluent-guest and soluent-host interactions. The latter are probably unimportant here as the solvent seems too bulky to compete with the guest. Moreover, neither solvophobic nor solvophilic forces are likely to contribute to K', significantly, since guest, host cavity, and solvent all are essentially lipophilic in character. When the guest is transferred from the bulk of the solvent to the host interior, the cavitation free energy for dissolution is released13 (AG, < 0), whereas no extra cavitation energy (>a)
CH30mH*0H '
1-0
4
(=I-ZI
3 In contrast to 3 which was sparingly soluble in all usual solvents, 2 was soluble in CH2C12,CHC13, and CHBr? and evaporation of the solutions yielded crystals with two molecules of solvent per host." The 'H NMR spectrum of the CHCl, complex in (CD(6) For a similar reaction, see ref 4c. (7) Canceill, J.; Collet, A.; Gottarelli, G . J . Am. Chem. SOC.1984, 106. 5997-6003. (8) Cage isomers 2 and 3 showed very different R, values with the following eluents on silica gel: CH,Cl,/acetone 9:1 ( R 0 47 and 0.05); CH2C12/acetone 8:2 (R, 0.86 and 0.08); CHC1,/CH30d95i5 (R, 0.84 and 0.52).
(9) Mass spectra taken at 70 eV on a ZAB-HF instrument, 'H NMR spectra on a Bruker AM2OOSY spectrometer. (IO) Canceill, J.; Collet, A,; Gabard, J.; Gottarelli,G.; Spada, G. P. J . Am. Chem. SOC.1985, 107, 1299-1308.
(1 1 ) As was observed4in cryptophane C and D, one of the solvent molecules is probably trapped in the host cavity and the other in voids of the lattice. The crystalline complexes of 2 turned out to be very stable and were not desolvated on prolonged heating (100-150 "C) under vacuum. (12) Models suggest that this solvent could enter the host cavity to form a highly strained, hence probably very unstable, complex; in principle" the true stability constant K, can be evaluated from K', if the stability of the solvent-host complex is known.
J. Am. Chem. SOC. 1986, 108, 4232-4233
4232
is required to enter the preorganized host; therefore, as was already pointed out,2bAGc should contribute to K', favorably. However, this term, which depends on the guest volume, is expected to increase on going from CHzC12 to CCl,, whereas the maximum stability is observed for the 2.CHC1, complex. This fact probably means that the contribution of AGc to the cavitate stabilization is relatively small. The high exothermal AH in the formation of the 2.CHC13 cavitate is certainly best interpreted in terms of overall attractive host-guest interactions, which in this case should mainly consist of multipole-multipole and dispersion forces. As these interactions are strongly distance-dependent, we should conclude that effective complementarity between guest and host has been achieved in this complex. We simply observe that in 2 (and also in l), the best guest, experimentally, has a size substantially smaller than that suggested from examination of CPK models. Moreover, complementarity seems to be a very sharp requirement, if we consider that the 2CHC1, cavitate is stabler than the CHzCl2and 1.O and 1.4 kcal/mol, respectively. CHBr3 ones by AG
-
(13) Cavity formation in solvents: see, for example: Stien, M. L.; Reisse,
J. Calorim. Anal. Therm. 1984, 15, 214-219 and references therein.
Diadamantylcarbene in Solution' David R. M y e r ~ , V~.. P. ~ Senthilnathan,4 Matthew S. plat^,*^,^ and Maitland Jones, Jr.*, Department of Chemistry, Princeton University Princeton, New Jersey 08544 Department of Chemistry, The Ohio State University Columbus, Ohio 43210 Received October 15, 1985 Revised Manuscript Received April 28, 1986
2
One of the substantial achievements of carbene chemistry has been the differentiation of singlet and triplet reactions. Diarylcarbenes have been the most often used vehicles for this work6 although the parent methylene6band carboalko~ycarbenes~ have also found use. Conspicuously absent are alkyl- and dialkylcarbenes and for good reason: their chemistry is most one-sided. The reactive singlet states are effectively trapped by the available intramolecular reactions and the reactions of the lower energy, generally ground state, triplets are rendered invisible. Even when entry to the singlet-triplet manifold is gained through the triplet by photosensitized irradiation of a precursor, the reactions of the less stable singlet often win Triplet di-tert-butylcarbene has been observed by Gano and d C of 1 and 2, r his collaboratorss at 14A K. WorkupHproduced 80%
of triplet carbene. Analysis of the zero-field parameters revealed a carbene surprisingly similar to methylene as the central bond angle was ca. 143O (triplet :CH2 = 137°).9 One must always bear in mind that the determination of angles from zero-field splitting parameters alone is not very reliable. We have found that diadamantylcarbene (4) not only is a triplet ground state with a wider central angle than di-tert-butylcarbene but shows substantial triplet reactivity even in solution at 25 OC. Irradiation of diadamantyldiazomethane1°labeled with I3C at the central position with an unfiltered 1000-W Hg-Xe lamp at 14 K produced a persistent triplet spectrum. Curie law analysis proved the triplet to be the ground-state species. The I3Chyperfine splitting could be observed and related to the central angle by using the model of Brandon et al." The hyperfine components of the high-field X and Y transitions and low-field Z transition are 252, 258, and 134 MHz, respectively. This compared with 282, 281, and 177 M H z for methylene.I2 Triplet diadamantylcarbene is long-lived in ethanol matrices between 4 and 75 K. In this respect it is even less reactive than diphenylcarbene. These values lead to a value of 152O, substantially wider than that in methylene12 and essentially the same as that in diphenylcarbene." A somewhat smaller angle of 146' can also be determined. At the suggestion of a referee we have analyzed the data by taking as the isotropic hyperfine interaction the average of the anisotropic hyperfine interactions oriented along the axes of the three zero-field transitions measured in our EPR experiment.12a If one assumes that one of the carbene orbitals is pure 2p (?) and the other an sp hybrid, the fractional s character of the hybrid orbital can be determined by using the correlation of either H i g ~ c h i ' , or ~ H a r r i ~ 0 n . I We ~ ~ suspect that the bond angle in di-tert-butylcarbene, reported to be 143°,8 is really larger as the zero-field parameters of 4 (D/hc = 0.6823 cm-I, E/hc = 0.038 cm-l) are nearly identical with those of di-tert-butylcarbene (D/hc = 0.689 cm-I, E/hc = 0.039 cm-l).s Irradiation of dry, degassed1, solutions of diadamantyldiazomethane in cis-2-butene at room temperature with a Hanovia medium-pressure mercury arc led to diadamantylmethane (5) as the major product (16% yield, 81% relative yield). The structure was confirmed by comparison with published datal0 although the position of the central methylene protons is not reported in the literature.I0 We have confirmed the unusually high upfield position of these protons ( 8 0.9) by synthesizing deuterio-5 from a-deuteriodiadamantylcarbinyl chloride. Small amounts of 1:1 adducts (4% yield, 19% relative yield) are also produced from 4 and cis-2-butene. The structures are tentatively assigned as 6 and 7 on the basis of their mass and IH NMR spectra.
4
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